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... Relative narrowness of the emission band detected from the curved side suggests that the alignment of the cholesteric layers at the interface with the polymer film is rather planar, i.e. parallel to the surface. The results presented in Ref.  indicate that thermal extrusion of the plastic films induces a well pronounced orientation effect for the polymer chains along the direction of the film extrusion. The liquid crystal molecules become aligned along this direction due to intermolecular forces. ...
... As a result, it is probable that the film surface has a wavy profile on a nanoscale. The geometrical profile that cancels degeneration along the tangential orientation of the director represents a much stronger factor, when compared to the intermolecular forces and the entropy effects of excluded volume . This also agrees with a higher quality of the planar alignment of cholesteric liquid crystal molecules at the polymer film surface. ...
We describe a compact point laser source based on dye-doped cholesteric encapsulated in a flexible polymer film. Optically pumped emission spectra of the capsule are experimentally studied.
... In all the abovementioned techniques, surface initiators are multifunctional surface modifiers-initiators where one functional group is able to graft to solid surfaces while another one is able to initiate surface-grafted polymerization at the same time (Fig. 3). In Fig. 3, the exemplary multifunctional surface modifiers-initiators for surface-initiated peroxide-mediated polymerization (a) and (b)  and for surface-initiated atom transfer radical polymerization (c)  are presented. Combinations of the different techniques of surface modification allow to modify almost all solid surfaces by grafted polymer brushes. ...
Temperature responsivity of polymer brushes may be driven by different mechanisms, from which the lower critical solution temperature (LCST) is the most famous one. The using of the grafted temperature-responsive polymer brushes based on LCST opens numerous opportunities for fabrication of “smart” or responsive surfaces. In this review, we try to join information on thermoresponsive and multi-responsive grafted polymer brushes with transitions based on LCST. The overwhelming majority of previously reported temperature-responsive grafted polymer brush coatings were based on PNIPAM and POEGMA, despite the fact that a wide range of other thermoresponsive polymers demonstrate similar properties. In this work, we not only give the detailed account for fabrication, mechanisms of action, and applications of well-known PNIPAM- and POEGMA-grafted brush coatings but also point to other types of thermoresponsive grafted brushes.
Photopolymer composites are the materials with wide application potential in paints and varnishes, diverse lithographic processes, electronics, medicine, and so forth. Here a new approach to the synthesis of macrophotoinitiators (MPIs) were developed and their effective application for curing polymer composites after immobilization on the surface of diverse mineral fillers was demonstrated. The MPIs were synthesized by reaction of benzoin or 3‐hydroxy‐1,2‐diphenyl‐2‐(propan‐2‐yloxy)propan‐1‐one as a photodissociating species with a copolymer of maleic anhydride with methyl methacrylate as carrier. Chemical structure of MPIs and the content of the tethered photoinitiating moieties were determined using 1NMR‐, IR‐, and UV‐spectroscopies. Photolysis of MPIs was investigated in details using a spot‐light curing system. It was demonstrated that MPIs are effective surface modifiers of mineral fillers, such as titanium dioxide, zinc oxide, and nanohydroxyapatite; and behave as effective photoinitiators. The benefits of using the fillers surface‐modified by MPIs in photo‐curable polymer composites were discussed.
Water-dispersed fluorescence nanomaterials based on boron nitride nanotubes and grafted copolymer brushes (poly(acrylic acid-co-fluorescein acrylate) were successfully fabricated in a two-step process. The functionalization of BNNTs was confirmed by spectroscopic, gravimetric and imaging techniques. In contrast to “pure” BNNTs, functionalized BNNTs demonstrate intense green fluorescence emission at 520 nm. The developed hybrid structure can potentially be used for cellular imaging, as “smart” surfaces, nanotransducers and nanocarriers.
Composition, thickness and properties of poly(4-vinylpyridine-co-oligo(ethylene glycol)ethyl ether methacrylate246) [P(4VP-co-OEGMA246)] copolymer grafted brush coatings attached to glass were studied in dry and swollen states using ellipsometry. These measured data are in good agreement with predicted (estimated) changes in the amount of water, refractive index and thickness of the grafted copolymer brush coatings at swelling. For POEGMA brushes the thickness of the coatings on swelling at 20 ˚C can be more than double, in contrast to P4VP where those changes are insignificant. Presence of 4VP units in the structure of the P(4VP-co-OEGMA246) copolymer grafted brushes significantly decreases the hydration degree even for coatings with very low concentrations of 4VP units.
The novel temperature-responsive poly(cholesteryl methacylate) (PChMa) coatings derived from renewable sources were synthesized and characterized. Temperature induced changes in wettability were accompanied by surface roughness modifications, traced with AFM. Topographies recorded for temperatures increasing from 5 to 25 °C showed a slight but noticeable increase of calculated root mean square (RMS) roughness by a factor of 1.5, suggesting a horizontal rearrangement in the structure of PChMa coatings. Another structural reordering was observed in the 55–85 °C temperature range. The recorded topography changed noticeably from smooth at 55 °C to very structured and rough at 60 °C and returned eventually to relatively smooth at 85 °C. In addition, temperature transitions of PChMa molecules were revealed by DSC measurements. The biocompatibility of the PChMa-grafted coatings was shown for cultures of granulosa cells and a non malignant bladder cancer cell (HCV29 line) culture.
Novel alignment coating with temperature-tuned anchoring for nematic liquid crystals (NLCs) was successfully fabricated in three step process, involving polymerization of poly(cholesteryl methacrylate) (PChMa) from oligoproxide grafted to the glass surface pre-modified with 3-aminopropyltriethoxysilane. Molecular composition, thickness, wettability of the PChMa coating and its alignment action for a NLC were examined with ToF-SIMS, ellipsometry, contact angle measurements, polarization optical microscopy and commercially produced PolScope technique allowing for mapping of the optic axis and optical retardance within the microscope field view. We find that PChMa coating provides specific monotonous increase (decrease) in the tilt angle of the NLC director with respect at the substrates normal on heating (cooling) referred to as anchoring tuning.
The surface alignment of lyotropic chromonic liquid crystals (LCLCs) can be
not only planar (tangential) but also homeotropic, with self-assembled
aggregates perpendicular to the substrate, as demonstrated by mapping optical
retardation and by three-dimensional imaging of the director field. With time,
the homeotropic nematic undergoes a transition into a tangential state. The
anchoring transition is discontinuous and can be described by a double-well
anchoring potential with two minima corresponding to tangential and homeotropic
It is shown that the attachment of macromolecules of the functional oligoperoxides to the planar polymeric surfaces or to the surface of a dispersed phase results in the localization of the peroxide groups on the interface. Designing of interphase layers with a well-defined structure and nature with the use of the peroxydized interphases and grafting reaction “to” and "from" the surface is carried out. The compatibilizing polymeric layers in polymeric blends and the grafting surface layers with special properties are formed.
To immobilize effectively oligonucleotide probes on SiO2 modified with (3-aminopropyl)triethoxysilane, four procedures based on streptavidin–biotin system are compared with Atomic Force Microscopy, Angle-Resolved X-ray Photoelectron Spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry. The first approach involves: adsorption of biotinylated Bovine Serum Albumin, blocking free surface sites with BSA, binding of streptavidin and biotinylated oligonucleotide (b-oligo). Final steps are exchanged in the second procedure with immobilization of preformed streptavidin–b-oligo conjugate. The third approach consists of streptavidin adsorption, blocking with BSA and b-oligo binding. Finally, streptavidin–b-oligo conjugate is immobilized directly within the fourth method. Surface coverage with biomolecules, determined from ARXPS, accords with average AFM height, and is anti-correlated with the intensity of Si+ ions. Higher biomolecular coverage was achieved during the last steps of the first (2.45(±0.38) mg/m2) and second (1.31(±0.22) mg/m2) approach, as compared to lower surface density resulting from the third (0.58(±0.20) mg/m2) and fourth (0.41(±0.11) mg/m2) method. Phosphorus atomic concentration indicates effectiveness of oligonucleotide immobilization. Secondary ions intensities, characteristic for oligonucleotides, streptavidin, BSA, and proteins, allow additional insight into overlayer composition. These measurements verify the ARXPS results and show the superiority of the first two immobilization approaches in terms of streptavidin and oligonucleotide density achieved onto the surface.
Thickness, refractive index and composition of coatings consisting of polymer brushes of poly(N-isopropyl acrylamide), fabricated with different polymerization times, and oligoperoxide, grafted to the glass surface with (3-aminopropyl)triethoxysilane, were determined using ellipsometry and AFM measurements at all the formation stages. Optimum grafting conditions were determined for each component of the composite film.Dry film measurements and in situ temperature depending swelling experiments were performed by multiple angle of incidence (MAI) ellipsometry. The temperature phase transition in water solution induced by collapse of the polymer brushes was detected using ellipsometry. The ability of coatings consisting of complex polymer brushes to modify physicochemical interfacial properties depending on temperature is demonstrated.
This study presents a new approach for developing biosensors based on enzymatic systems with designed three-dimensional structures. Silica glass slides were chemically functionalized at surfaces by reacting with organosilanes, 3-mercaptopropyltriethoxysilane (MPTES), and 3-aminopropyltriethoxysilane (APTES), using sol–gel process at room temperature. The functionalization of the supports was characterized by contact angle measurements and FTIR spectroscopy. The first enzyme layer was covalently immobilized to the support by a bi-functional linker (glutaraldehyde). The second enzyme layer was deposited using the protein conjugation method based on the high affinity “avidin–biotin” interactions. Each enzyme was biotinylated before being added to the nanostructured system and avidin was used as the binder between consecutive enzyme layers. The biochemical response was assayed at all stages to certify that the enzymatic bioactivity was retained throughout the entire layer-by-layer (LBL) process. The model of building 3D-enzymatic systems was evaluated using the enzymatic structure with glucose oxidase (GOx) and horseradish peroxidase (HRP). It was verified that the amino-modified support presented the highest bioactivity response compared to the other chemical functionalities. Moreover, the bienzyme nanostructure demonstrated relevant biochemical activity upon injecting the glucose substrate into the system. Finally, as a proof of concept, the bienzyme systems were assayed using real samples of regular and sugar-free soft drinks where they effectively behaved as structured biosensor for glucose with the built-in 3D hybrid architecture. Based on the results, it can be foreseen the development of promising new nanomaterials for several analytical applications such as monitoring the quality of food and beverages for nutrition purposes.
—When K. L. Mittal asked me to provide a historical account of the applications of silane coupling agents in adhesion, I decided to write in the form of a personal account of my last 45 years in this line of study. No attempt is made to make the history comprehensive, or to recognize the host of other researchers who have contributed to our understanding of adhesion across an interface of dissimilar materials. It has been an immensely interesting area of study with many practical applications in composites and bonded structures.
BACKGROUND: Peroxidation of a poly(ethylene terephthalate) (PET) surface clears the path to the formation of biospecific polymeric layers on it. The goal of this work was the modification of a PET surface with oligoperoxides with further grafting of dextran macromolecules to this peroxidated surface.
RESULTS: Novel oligoperoxides with a good affinity to PET were synthesized. They are capable of attaching to the PET surface, due to the decomposition of peroxide groups via the formation of free radicals. The alterations in surface energy and its components as a result of surface modification as well as changes in topography of the PET surface were determined. The degree of modification of the PET surface can reach 68% and depends on the following: the method of oligoperoxide and dextran deposition; the concentration of both oligoperoxide and dextran in the initial solution; and the temperature at which the modification is carried out.
CONCLUSION: A new method of PET surface activation has been developed. The attachment of dextran macromolecules to modified PET surfaces is confirmed. Copyright
The use of blood as DNA source to be employed in genetic analysis requires a purification process in order to remove proteins, lipids and any other contaminants, such as hemoglobin, which inhibit PCR. On the other hand, the increasing demand of miniaturized and automated biological tests able to reduce time and cost of analysis, requires the development and the characterization of materials aimed to perform the DNA purification processes in micro-devices. In this work we studied the interaction of DNA molecules with modified silicon based substrates, positively charged after deposition of a (3-aminopropyl)triethoxysilane (APTES) or 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AEEA) interfacial layer. The evaluation of the DNA adsorption and elution capacity of different substrates (thermally grown silicon oxide, silicon oxide obtained by plasma enhanced chemical vapour deposition, and Pyrex®) was studied taking into account the nature of the substrate and the effect of DNA length (in the 208–50,000 base pairs range). Main findings are that DNA elution capacity depends both on the utilized substrate and on the choice of the silanizing agent. Higher DNA recovery was obtained from AEEA-modified substrates, but the eluted DNA had different electrophoretic properties from native DNA. DNA with the same electrophoretic behaviour as genomic DNA was instead recovered from APTES-treated surfaces. Furthermore, the length of DNA present in the starting material strongly modulates the elution efficiency, longer DNA being released in a lesser amount, suggesting that opportunely modified surfaces could be used as systems for differential DNA separation.
Amino-modified metal oxide materials are essential in a wide range of applications, including chromatography, ion adsorption, and as biomaterials. The aim of this study is to compare different functionalization techniques on a selection of metal oxides (i.e. SiO2, TiO2, ZrO2, and SnO2) in order to determine which combination has the optimal properties for a certain application. We have used the nanocasting approach to synthesize micrometer-sized TiO2, ZrO2, and SnO2 particles, which have similar morphologies and porosities as the starting mesoporous SiO2 microparticles (Lichroprep Si 60). These metal oxides were subsequently functionalized by four different approaches: a) covalent bonding of 3-aminopropyltriethoxysilane (APTES), b) adsorption of 2-aminoethyl dihydrogen phosphate (AEDP), c) surface polymerization of aziridine (AZ), and d) electrostatic interaction of polyethyleneimine (PEI) to produce a high surface coverage of amino groups on their surfaces. Scanning electron microscopy, nitrogen physisorption and X-ray diffraction were used to characterize the unmodified metal oxide particles, while thermogravimetric analysis, ninhydrin adsorption and zeta potential titrations were applied to gain insight into the successfulness of the various surface modifications. Finally, the hydrolytic stability at pH 2 and 10 was investigated using zeta potential measurements. Unfortunately, the AEDP approach was not able to produce an efficient amino-modification on any of the tested metal oxide surfaces. On the other hand, modifications with APTES, aziridine and PEI appeared to give fairly stable amino-functionalizations at high pH values for all metal oxides, while these modifications were easily detached at pH 2, with the exception of SnO2 where the AZ and PEI samples were stable up to 40 h. The results are expected to give valuable insights into the possibility of replacing amino-modified silica with more hydrolytically stable metal oxides in various application fields, for example chromatography and drug delivery.
A short review is given of successively the diamagnetic susceptibility, the refractive index, the dielectric permittivity, the elastic constants and the viscosity coefficients of nematic liquid crystals. Emphasis is on typical results that have been obtained, and the possibilities and problems connected with a molecular interpretation. In particular an attempt is made to distinguish in the macroscopic quantity the influence of the molecular properties involved, of the direct temperature dependence, and of the dependence on the orientational order (indirect temperature dependence).
We report the results of probing adhesion and friction forces between surfaces with functional terminal groups with chemically modified scanning probe microscopy (SPM) tips. Surfaces with terminal groups of CH3, NH2, and SO3H were obtained by direct chemisorption of silane-based compounds on silicon/silicon nitride surfaces. We studied surface properties of the resulting self-assembled monolayers (SAMs) in air and aqueous solutions with different pHs. Work of adhesion, “residual forces”, and friction coefficients was obtained for four different types of modified tips and surfaces. Absolute values of the work of adhesion between various surfaces, Wad, were in the range 0.5−8 mJ/m2. The work of adhesion for different modified surfaces correlated with changes of solid−liquid surface energy estimated from macroscopic contact-angle measurements. Friction properties varied with pH in a register with adhesive forces showing a broad maximum at intermediate pH values for a silicon nitride/silicon nitride mating pair. Similar broad maxima were observed in the acid range for a NH2-terminated SAM and in the basic range for a SO3H-terminated SAM. This behavior can be understood considering the changes of the surface charge state determined by the zwitterionic nature of silicon nitride surfaces with multiple isoelectric points.
Poly(N-isopropylacrylamide) (PNIPAM) coatings attached to glass with novel approach involving polymerization from oligoperoxide grafted to surface with (3-aminopropyl)triethoxysilane exhibit not only temperature- but also pH-dependence of wettability and protein adsorption. Wettability and composition of coatings, fabricated with different polymerization times, were determined using contact angle measurements and Time Of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS), respectively. Thermal response of wettability, measured between 20 and 40°C, was prominent at pH 9 and 7 and diminished or absent at pH 5 and 3. This indicates a transition between hydrated loose coils and hydrophobic collapsed chains that is blocked at low pH. Higher surface roughness and dramatically increased adsorption of model protein (lentil lectin labeled with fluorescein isothiocyanate) were observed with AFM and fluorescence microscopy to occur in hydrophobic phases (at pH 3, for pH varied at constant temperature of 22°C and at ∼33°C, for temperature varied at constant pH 9). Protein adsorption response to pH was confirmed by TOF-SIMS and Principal Component Analysis.
We report a first observation of nanoscale surface structures of segregated pinned micelles of grafted Y-shaped molecules and their reversible structural reorganization. We designed a novel type of Y-shaped molecules combining two highly incompatible polymer chains (arms) attached to a single focal point capable of chemical grafting to a functionalized silicon surface. We demonstrated that spatial constraints induced by a chemical junction of two dissimilar (hydrophobic and hydrophilic) polymer arms in such Y-shaped molecules lead to the formation of a novel type of segregated pinned micellar structures in chemically grafted brush layers. We propose a model of segregated pinned micelles and corresponding reverse micelles featuring different segregation states of polystyrene and poly(acrylic acid) arms. These arms are capable of local reversible rearrangements leading to reversible surface structural reorganization in different solvents.
Gas adsorption (physisorption and chemisorption) in the monolayer range on silicon and germanium surfaces was studied by means of ellipsometry and the results were compared with volumetric adsorption measurements on powders. Using these data together with literature values of atomic polarizabilities and Van der Waals diameters, good agreement was found between observed and calculated values of the ellipsometric effect. A review is given of the theories concerning ellipsometry, especially in the sub-monolayer region. In the chemisorption experiments an anomalous change was observed in one of the ellipsometrically determined angles (ψ). This is explained by assuming that the clean silicon or germanium crystal has a very thin (10 Å) optically absorbing surface layer, which becomes less absorbing due to the chemisorption process.Comparison of the ellipsometric results of chemisorption experiments on Si (111) and Si (100) surfaces showed that several gases adsorb twice as much on Si (100), whereas other gases adsorb in the same amounts on both surface planes.
An approach to determine structural features, such as surface fractional coverage F and thickness d of protein layers immobilized on silicon substrates coated with amino-organic films is presented. To demonstrate the proposed approach rabbit gamma globulins (RgG) are adsorbed from a 0.66muM solution onto SiO(2) and Si(3)N(4) modified with (3-aminopropyl)triethoxysilane (APTES). Atomic force microscopy data are analyzed by applying an integral geometry approach to yield average coverage values for silanized Si(3)N(4) and SiO(2) coated with RgG, F=0.99+/-0.01 and 0.76+/-0.08, respectively. To determine the RgG thickness d from angle-resolved X-ray photoelectron spectroscopy (ARXPS), a model of amino-organic bilayer with non-homogeneous top lamellae is introduced. For an APTES layer thickness of 1.0+/-0.1nm, calculated from independent ARXPS measurements, and for fractional surface RgG coverage determined from AFM analysis, this model yields d=1.0+/-0.2nm for the proteins on both silanized substrates. This value, confirmed by an evaluation (1.0+/-0.2nm) from integral geometry analysis of AFM images, is lower than the RgG thickness expected for monomolecular film ( approximately 4nm). Structures visible in phase contrast AFM micrographs support the suggested sparse molecular packing in the studied RgG layers. XPS data, compared for bulk and adsorbed RgG, suggest preferential localization of oxygen- and nitrogen-containing carbon groups at silanized silicon substrates. These results demonstrate the potential of the developed AFM/ARXPS approach as a method for the evaluation of surface-protein coverage homogeneity and estimation of adsorbed proteins conformation on silane-modified silicon substrates used in bioanalytical applications.
Polymer brushes, which are ultrathin polymer coatings consisting of polymer chains that are tethered with one chain end to an interface, prepared through surface-initiated controlled radical polymerization (SI-ATRP) was studied. A significant increase in the rate of SI-ATRP was observed for polymerizations carried out in polar and, in particular, aqueous media. SI-RATRP was successfully used by Sedjo to prepare PS and PS-b-PMMA brushes from a conventional radical azo-functionalized silica substrate using Cu IIBr2/bpy complex as deactivating agent. Surface-initiated nitroxide-mediated polymerization (SI-NMP) also represents a valuable method for the controlled fabrication of polymer brushes. The variety of polymerization techniques, postmodification strategies, and patterning methods together with the ongoing advances in each of these areas indicates that there is still plenty of room for future developments.
We consider a three dimensional liquid drop sitting on a rough and chemically heterogeneous substrate. Using a novel minimization technique on the free energy of this system, a generalized Young's equation for the contact angle is found. In certain limits, the Cassie and Wenzel laws, and a new equivalent rule, applicable in general, are derived. We also propose an equation in the same spirit as these results but valid on a more `microscopic' level. Throughout we work under the presence of gravity and keep account of line tension terms.